Overview

S21800 is a nitrogen-strengthened, high-silicon, high-manganese austenitic chromium-nickel stainless steel (nominally 17% chromium, 8.5% nickel, 8% manganese, 4% silicon — the "17-8-8" type) developed primarily as a wear- and galling-resistant alloy. This datasheet presents the material within the American standard system.

It is fully austenitic, and the deliberate additions of silicon and manganese create a matrix that inhibits wear, galling and fretting even in the annealed condition — giving wear and galling resistance comparable to cobalt-based (Stellite-type) alloys but without the cost or machining difficulty of a cobalt alloy. Its room-temperature yield strength is approximately twice that of Types 304 and 316. The general corrosion resistance falls between Types 304 and 316, but it offers superior chloride-pitting, stress-corrosion-cracking and crevice-corrosion resistance to Type 316, and its high-temperature oxidation resistance is similar to Type 309, with useful properties to about 982 °C (1800 °F). It also retains good impact toughness at low temperature and is essentially non-magnetic. Cold work raises strength and hardness but does not further enhance the anti-galling behaviour, which is inherent in the annealed matrix.

Typical applications include valve stems, seats and trim, fastening systems, pins, bushings and roller bearings, pump shafts and rings, wear rails and screening — particularly where galling or seizure must be avoided without resorting to cobalt- or high-nickel-based hardfacing.

1. Physical Properties

Values per manufacturer / reference data, annealed condition.

2. Chemical Composition (wt %)

Limiting composition per ASTM A276 / AMS 5848.

Nominal: 17Cr-8.5Ni-8Mn-4Si with nitrogen. The combination of high silicon and manganese is the defining feature — it creates a matrix that resists galling, wear and fretting in the annealed condition, while nitrogen and manganese provide the high strength.

3. Mechanical Properties

Typical room-temperature properties, annealed condition.

Room-temperature yield strength is about twice that of Types 304 and 316. Cold work raises strength and hardness (the alloy stays fully austenitic after severe cold work) but does not further improve the anti-galling behaviour. Values are typical; confirm against the mill test certificate.

4. Corrosion, Wear and High-Temperature Resistance

In a wear system, galling/seizure typically fails first, then wear, then corrosion — so galling and wear resistance are the primary design drivers for this alloy.

5. Heat Treatment

An austenitic stainless steel; it cannot be hardened by heat treatment. High strength comes from nitrogen, manganese and silicon; strength and hardness can be raised by cold work (without improving the inherent anti-galling behaviour).

Solution Anneal approximately 1040–1120 °C, followed by rapid cooling (water quench), to dissolve carbides and produce a uniform austenitic structure; the anti-galling matrix is fully developed in this annealed condition.

The alloy remains fully austenitic and essentially non-magnetic even after severe cold work. Hot working is done in the range ~1095–1175 °C (2000–2150 °F).

6. Weldability and Joining

Can be handled in the weld shop like Types 304 and 316, using a matching Nitronic 60W bare wire — included in AWS A5.9 as ER218. No preheat or post-weld heat treatment is normally required other than normal stress relief in heavy fabrication. Most applications are used in the as-welded condition (except where corrosion resistance governs). Autogenous (fillerless) gas-tungsten-arc fusion welds can be made; such welds are free from cracking and retain galling and cavitation resistance similar to the base metal.

No preheat or post-weld heat treatment normally required.

7. Machinability and Fabrication

Machining Guidelines

Forming Processes

8. Applications

9. Available Product Forms and Standards

Nitrogen-strengthened high-silicon high-manganese 17-8-8 wear- and galling-resistant austenitic stainless steel. UNS S21800; AMS 5848; ASTM A276 / A193; AWS A5.9. Tradenames: Nitronic 60, Alloy 218, Gall-Tough Plus.

10. Comparison with Related Alloys (UNS System)

Next：Alloy 218